Electric machine with stator having even slot distribution

ABSTRACT

A multi-phase electric machine having plurality of windings are mounted on the stator core that define a plurality of phases wherein, for each phase, the windings include at least two parallel windings, each winding comprising a pair of continuous wires which are connected in series. For each pole, the parallel windings fill one or more central slots and two outer slots. Each winding fills each central slot twice the number of times that the winding fills each outer slot to thereby define a slot fill ratio of 2:1 between central slots and outer slots and wherein each wire of the wire pair forming a winding fills the slots in a ratio that differs from the slot fill ratio. Phase shift end loops shift the windings from one outer slot to the other outer slot. Position change end loops alter the relative positions of the parallel windings.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119(e)of U.S.provisional patent application Ser. No, 62/368,070 filed on Jul. 28,2016 entitled ELECTRIC MACHINE WITH STATOR HAVING PHASE SHIFT WINDINGS;U.S. provisional patent application Ser. No. 62/368,104 filed on Jul.28, 2016 entitled ELECTRIC MACHINE WITH STATOR HAVING EVEN SLOTDISTRIBUTION; and U.S. provisional patent application Ser. No.62/373,223 filed on Aug. 10, 2016 entitled ELECTRIC MACHINE WITH STATORWINDINGS HAVING OVER-UNDER END LOOPS; the disclosures of each of whichare hereby incorporated herein by reference.

BACKGROUND

The present invention relates to electric machines.

Electric machines are used for several different purposes in modernvehicles. For example, electric machines are commonly employed asstarters, alternators, traction motors and for other purposes. In theseapplications, the electric machine may act as a motor, generator or beselectively operable as either a motor or a generator.

There is an increasing demand for electric machines used in vehicleapplications, as well as other non-vehicular applications, for anelectric machine with reduced size and increased efficiency.

Improvements in electric machine design which allow for cost efficientmanufacture while meeting the increasingly stringent demands of modernvehicular applications are desirable.

SUMMARY

The present invention provides an electric machine with an improvedwinding pattern that can be efficiently manufactured and provides acompact and efficient electric machine.

The invention comprises, in one form thereof, a multi-phase electricmachine that includes a stator operably coupled with a rotor wherein therotor is rotatable relative to the stator. The stator includes a statorcore defining a central opening and a plurality of axially extendingslots which circumscribe the central opening. A plurality of windingsare mounted on the stator core wherein the plurality of windings definea plurality of phases and wherein, for each phase, the plurality ofwindings include at least two parallel windings, each winding comprisinga pair of continuous wires which are connected in series. For each pole,the parallel windings are disposed in one or more central slots and twoouter slots disposed on opposite sides of the central slots. Eachwinding is disposed in each of the central slots an equal number oftimes and is disposed in each of the outer slots an equal number oftimes and wherein each winding is disposed in each central slot twicethe number of times that the winding is disposed in each outer slot tothereby define a slot fill ratio of 2:1 between central slots and outerslots and wherein each wire of the wire pair forming a winding isdisposed in the slots in a ratio that differs from the slot fill ratio.

In some embodiments, for each pole for at least one winding, a first oneof the outer slots is disposed on one of the clockwise orcounterclockwise sides of the central slots and a second one of theouter slots is disposed on the opposite side of the central slots andwherein one of the pair of continuous wires connected in series to formthe at least one winding has a first wire and a second wire with thefirst wire being the only one of the first and second wires that isdisposed in the first one of the outer slots. In some embodiments, thesecond wire is the only one of the first and second wires that isdisposed in the second one of the outer slots. In some embodiments, eachwinding is disposed in each of the slots an equal number of times.

In some embodiments, the stator assembly defines a standard pitchbetween each pole of each phase, the pitch being a commoncircumferential spacing between corresponding slots of each pole, andwherein each wire includes a phase shift end loop having a pitch thatdiffers from the standard pitch by one slot, each of the parallelwindings having the phase shift end loop at the same pole locations.This shifts the parallel windings from one outer slot to the other outerslot.

in such an embodiment, the stator assembly may define first and secondoppositely disposed axial ends, each of the windings defining leadsconnectable to an external circuit member, the leads being disposed atthe first axial end and the phase shift end loops being disposed at thesecond axial end. In still further embodiments, each wire may extend fora plurality of wraps about the stator with the phase shift end loopsbeing disposed at a location where the wire transitions from one layerto another layer.

In some embodiments, the stator assembly defines a winding patternwherein, for each pole of each phase, a first one of the outer slots isdisposed on the counterclockwise side of the central slots and a secondone of the outer slots is disposed on the clockwise side of the centralslots and wherein the wires disposed in one of the first and secondouter slots are disposed in the radially outermost layers and the wiresin the other one of the first and second outer slots are disposed in theradially innermost layers whereby each outer slot is filled with wiresfrom two separate phases,

In some embodiments, each wire includes at least one position change endloop, wherein each of the parallel windings has one of the positionchange loops at the same location, wherein the position change end loopsdefine a non-standard pitch to thereby change the relative positions ofthe parallel windings in the slots. In such an embodiment, the statorassembly may define first and second oppositely disposed axial ends,each of the windings defining leads connectable to an external circuitmember, the leads and the position change end loops being disposed atthe first axial end and the phase shift end loops being disposed at thesecond axial end. In some embodiments, each phase of such an electricmachine may include at least three windings connected in parallel.

In an embodiment having at least three windings connected in parallel,some embodiments include a stator assembly having three parallelwindings for each phase wherein each pole includes two central slots andtwo outer slots, each central slot being filled with six segments ofwire and each outer slot being filled with three segments of wire. Insuch an embodiment, each wire of each winding of each phase may defineone phase shift end loop and three position change end loops with allremaining end loops defining a standard pitch. Such an embodiment mayinclude a stator assembly that defines first and second oppositelydisposed axial ends with each of the windings defining leads connectableto an external circuit member, the leads and the position change endloops being disposed at the first axial end and the phase shift endloops being disposed at the second axial end. Such an embodiment mayhave a stator assembly wherein, for each pole of each phase, a first oneof the outer slots is disposed on the counterclockwise side of thecentral slots and a second one of the outer slots is disposed on theclockwise side of the central slots and wherein the wires disposed inone of the first and second outer slots are disposed in the radiallyoutermost layers and the wires in the other one of the first and secondouter slots are disposed in the radially innermost layers whereby eachouter slot is filled with wires from two separate phases. Such anembodiment may take the form of a three phase electric machine.

The invention comprises, in another form thereof, a multi-phase electricmachine that includes a stator operably coupled with a rotor wherein therotor is rotatable relative to the stator. The stator includes a statorcore defining a central opening and a plurality of axially extendingslots which circumscribe the central opening. A plurality of windingsare mounted on the stator core wherein the plurality of windings definea plurality of phases. For each phase, the plurality of windings includeat least two parallel windings, each winding includes a pair ofcontinuous wires which are connected in series and fill an equal numberof slots. For each pole, the parallel windings fill one or more centralslots and two outer slots disposed on opposite sides of the centralslots, the number of windings in each phase being equal to one less thanthe total number of central and outer slots. Each winding fills each ofthe central slots an equal number of times and fills each of the outerslots an equal number of times and wherein each winding fills eachcentral slot twice the number of times that the winding fills each outerslot to thereby define a slot fill ratio of 2:1 between central slotsand outer slots. Each wire of the wire pair fills the slots in a ratiothat differs from the slot fill ratio. The parallel windings aredisposed in adjacent slots leaving one outer slot empty at each pole foreach wrap and each wire extends for a plurality of wraps about thestator. The stator assembly defines a standard pitch between each poleof each phase, the pitch being a common circumferential spacing betweencorresponding slots of each pole. Each wire includes a phase shift endloop having a pitch that differs from the standard pitch by one slot;each of the parallel windings having the phase shift end loop at thesame pole locations whereby the phase shift end loops shift the parallelwindings from one of the outer slots to the other outer slot. The statorassembly defines first and second oppositely disposed axial ends, eachof the windings defining leads connectable to an external circuitmember, the leads being disposed at the first axial end and the phaseshift end loops being disposed at the second axial end.

In such an embodiment, the phase shift end loops may be disposed at alocation where the wire transitions from one layer to another layer. Thephase shift end loops may also define a pitch one slot greater than thestandard pitch.

The windings of each phase may include at least three windings connectedin parallel. In such an embodiment having three parallel windings, eachpole may include two central slots and two outer slots with each centralslot being filled with six segments of wire and each outer slot beingfilled with three segments of wire. In some embodiments of such anelectric machine, the stator assembly may be configured such that, foreach pole of each phase a first one of the outer slots is disposed onthe counterclockwise side of the central slots and a second one of theouter slots is disposed on the clockwise side of the central slots andwherein the wires disposed in one of the first and second outer slotsare disposed in the radially outermost layers and the wires in the otherone of the first and second outer slots are disposed in the radiallyinnermost layers whereby each outer slot is filled with wires from twoseparate phases.

Such an embodiment may take the form of a three phase electric machine.It may also include phase shift end loops that are disposed at alocation where the wire transitions from one layer to another layer andhave phase shift end loops that define a pitch one slot greater than thestandard pitch.

The invention comprises, in another form thereof, a multi-phase electricmachine that includes a stator operably coupled with a rotor wherein therotor is rotatable relative to the stator. The stator includes a statorcore defining a central opening and a plurality of axially extendingslots which circumscribe the central opening. A plurality of windingsare mounted on the stator core wherein the plurality of windings definea plurality of phases and wherein, for each phase, the plurality ofwindings include at least two parallel windings. Each winding includes apair of wires which are connected in series and, for each pole, theparallel windings are disposed in one or more central slots and twoouter slots disposed on opposite sides of the central slots. For atleast one winding, the pair of wires forming the winding are connectedin series by a reversing loop and, for each pole for the at least onewinding, a first one of the outer slots is disposed on one of theclockwise or counterclockwise sides of the central slots and a secondone of the outer slots is disposed on the opposite side of the centralslots and one of the pair of continuous wires connected by the reversingloop to form the at least one winding has a first wire and a second wirewith the first wire being the only one of the first and second wiresthat is disposed in the first one of the outer slots.

In some embodiments, the second wire is the only one of the first andsecond wires that is disposed in the second one of the outer slots. Insuch an embodiment, for at least one central slot of one pole, the firstand second wires may be disposed in the same slot. Such embodiments mayfurther be configured such that, for each pole, the parallel windingsare disposed in the one or more central slots and the two outer slotsdisposed on opposite sides of the central slots with each windingdisposed in each of the central slots an equal number of times anddisposed in each of the outer slots an equal number of times and whereineach winding is disposed in each central slot twice the number of timesthat the winding is disposed in each outer slot to thereby define a slotfill ratio of 2:1 between central slots and outer slots and wherein eachwire of the wire pair forming one of the parallel windings are disposedin the slots in a ratio that differs from the slot fill ratio.

The invention comprises, in still another form thereof, a multi-phaseelectric machine htat includes a stator operably coupled with a rotorwherein the rotor is rotatable relative to the stator. The statorincludes a stator core defining a central opening and a plurality ofaxially extending slots which circumscribe the central opening. Aplurality of windings are mounted on the stator core wherein theplurality of windings define a plurality of phases and wherein, for eachphase, the plurality of windings include at least two parallel windings.Each winding includes a pair of wires which are connected in series and,for each pole, the parallel windings are disposed in one or more slots.A first one of the parallel windings has a first pair of the wires, thefirst pair of wires being connected in series by a reversing loop,wherein the first one of the parallel windings is electrically balancedand at least one wire of the first pair of wires is electricallyunbalanced.

In one embodiment, the first parallel winding is disposed in one or morecentral slots and two outer slots disposed on opposite sides of thecentral slots, and wherein, for each pole for of the first parallelwinding, a first one of the outer slots is disposed on one of theclockwise or counterclockwise sides of the central slots and a secondone of the outer slots is disposed on the opposite side of the centralslots and wherein the pair of continuous wires connected by thereversing loop to form the first parallel winding has a first wire and asecond wire with the first wire being the only one of the first andsecond wires that is disposed in the first one of the outer slots. Insuch an embodiment, the second wire may be the only one of the first andsecond wires that is disposed in the second one of the outer slots.

In some embodiments, for each pole, the parallel windings are disposedin one or more central slots and two outer slots disposed on oppositesides of the central slots with each winding disposed in each of thecentral slots an equal number of times and disposed in each of the outerslots an equal number of times and wherein each winding is disposed ineach central slot twice the number of times that the winding is disposedin each outer slot to thereby define a slot fill ratio of 2:1 betweencentral slots and outer slots and wherein each wire of the wire pairforming one of the parallel windings are disposed in the slots in aratio that differs from the slot fill ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features of this invention, and the mannerof attaining them, will become more apparent and the invention itselfwill be better understood by reference to the following description ofan embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a partial winding diagram showing three wires defining a partof an individual phase.

FIG. 2 is a partial winding diagram showing three wires that areconnected in series with the wires depicted in FIG. 1 to form anindividual phase.

FIG. 3 is a top view of a stator diagram illustrating the arrangement ofthe wires of FIGS. 1 and 2.

FIG. 4 is a detail view of a portion of the stator diagram of FIG. 3.

FIG. 5 is another detail view of a portion of the stator diagram of FIG.3.

FIG. 6 is a cross sectional view of an electric machine.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the exemplification set outherein illustrates an embodiment of the invention, in one form, theembodiment disclosed below is not intended to be exhaustive or to beconstrued as limiting the scope of the invention to the precise formdisclosed.

DETAILED DESCRIPTION

FIG. 6 illustrates an electric machine 20. In the illustratedembodiment, electric machine 20 is an automotive alternator capable ofoperating as a motor or as a generator, however, alternative embodimentsmay take the form of an electric machine that is solely operable as amotor or solely operable as a generator. Electric machine 20 includes arotor 22 mounted on a shaft 24 which both rotate relative to stator 26.Stator 26 has a stator core 28 and a plurality of windings 30.

Stator core 28 may be formed out of a stack of laminations and defines aplurality of slots 32. Windings 30 include axially extending segments 34that are disposed within slots 32 and end turns 36 with each end turn 36connecting a pair of slot segments 34. Axially extending slots 32circumscribe central opening 38 of stator core 28.

The illustrated embodiment is a three phase electric machine with sixturns. Additionally, each phase includes three windings arranged inparallel. In other words, each winding extends about the fullcircumference of the stator core six times and there are three suchwindings for each phase. To achieve this arrangement two separate wiresor filars are used for each winding whereby a total of six separatewires or filars are used for each phase. Each of the individual wiresform three turns about the stator and is connected in series withanother one of the wires to thereby form one of the three windings ofeach phase.

One parameter that may be used to describe a winding arrangement isslots per pole per phase. This is equal to the number of slots per polein each slot group of the winding if each such slot were filled solelyby windings of one phase. For example, in the illustrated embodiment,there are 18 slot segments in each slot group and each slot holds 6 slotsegments therefore the illustrated arrangement has 3 slots per pole perphase. The illustrated embodiment, however, has what is known as a phaseshift and some slots hold slot segments of two different phases.

The use such phase shifting can reduce what is known as the skin effect.As a general rule, when the conductors in a particular slot carrydifferent phase currents, the skin effect in such conductors will beless than if all of the conductors in the slot carried the same phasecurrent. While such phase shifting reduces the skin effect, the use ofsuch phase shifting can make it more difficult to electrically balancethe windings.

To avoid or minimize a re-circulating current in the winding, it isdesirable for the winding to be electrically balanced this isparticularly true for a winding having a plurality of wires connected inparallel. Providing an electrically balanced stator can be particularlydifficult if phase shifting is employed and each phase is formed by anodd number of windings arranged in parallel.

The illustrated embodiment provides a stator winding pattern whichprovides an electrically balanced stator with phase shifting and an oddnumber of windings arranged in parallel for each phase. As mentionedabove, the illustrated winding pattern includes six turns and threeseparate windings for each phase. The pattern has three slots per poleper phase but windings occupy four physical slots for each pole or slotgroup. In each slot group, the two center slots each have six conductorswhich are all from the same phase. The two outer slots each have threeconductors from one phase and three additional conductors from adifferent phase. To electrically balance the stator, each slot of theslot group needs to have an equal number of conductors from each of thethree windings. It is also desirable for each of the different radiallayers to have an equal number of conductors from each of the threewindings. This radial balancing, however, is less important than thebalancing between slots. The exemplary winding pattern can be used toprovide an electrically balanced stator and is further described belowwith the aid of FIGS. 1-5.

FIG. 1 illustrates three separate wires X, Y, Z that are connected inseries with the three separate wires A, B, C illustrated in FIG. 2. Morespecifically, wire A is connected in series with wire Z to form a firstwinding, wire B is connected in series with wire X to form a secondwinding and wire C is connected in series with wire Y to form a thirdwinding. The first, second and third windings are then connected inparallel to form one phase of electric machine 20. Electric machine 20is a three phase electric machine and two additional phases having thesame winding arrangement are also employed with electric machine 20,

As can be seen in FIG. 3, each phase of the stator assembly defines 16poles with each pole being formed by four physical slots. Six wires fitwithin each axially extending stator slot 32. As used herein, theradially outermost wire is in layer 1, layer 2 being the next radiallyinward wire position and so on with the radially innermost wire positionbeing layer 6.

As can also be seen in FIG. 3, as well as FIGS. 4 and 5, each of thepoles is formed by a group of four slots wherein the two central slotsare each completely filled with windings (six windings in theillustrated embodiment) and two outer slots that are only half filledwith windings from a particular phase (three windings in the illustratedembodiment) to thereby form a 3-6-6-3 winding pattern. As used herein,and as labelled in FIG. 4 for slot 15 and slot 3, starting at the outerslot on the counterclockwise side of each slot group forming a pole andmoving clockwise, the slots are referred to as slot AA, slot BB, slot CCand slot DD. In other words, slots BB and CC form the central slots andslots AA and DD form the outer slots.

The distance between slot AA of one pole and slot AA of the adjacentpoles is 9 slots. Similarly, the distance between slot BB of one poleand slot BB of the adjacent poles is 9 slots and so on, this distancebetween corresponding slots of the slot groups forming adjacent polesdefines the standard pitch of the electric machine. In the illustratedembodiment, the standard pitch is 9 slots.

Returning to FIGS. 1 and 2, the wiring diagrams label any pitch betweenslot segments that is non-standard. The location of the numberindicating the non-standard pitch also indicates at which axial end ofthe stator the end loop forming the non-standard pitch is located. It isalso noted that the wiring diagrams of FIGS. 1 and 2 also indicate inwhich layer position the wires are located.

As most easily seen in FIGS. 3-5, the windings in slot AA are positionedin the radial outermost layers, i.e., layers 1, 2 and 3 while thewindings in slot DD are positioned in the radial innermost layers, i.e.,layers 4, 5 and 6. When all of the phases have this same pattern, slotAA of one phase will correspond and overlap with slot DD of an adjacentphase allowing the outer slots to be completely tilled with windings.FIGS. 3-5 illustrate the windings of only one phase except for the spacebetween poles 2 and 3 of FIG. 4. This portion of FIG. 4 illustrates thelocation of the windings from a second phase (indicated by filled-inwire outlines) and the location of the windings from a third phase(indicated by the hollow wire outlines). This clearly shows how theouter slots of each phase overlap such that each outer slot includeswindings from two different phases.

It is further noted that while the outer slots of the illustratedembodiment have windings wherein the windings from one phase are allpositioned in the radially outer most layers and the windings from theother phase are all positioned in the radially innermost layers, otherconfigurations are also possible. For example, the windings from thedifferent phases could alternate. In the illustrated embodiment thiscould be achieved by having windings in layers 1, 3 and 5 in slot AA andin layers 2, 4 and 6 in slot DD. Such an arrangement, however, would bemore difficult to manufacture than the illustrated embodiment and wouldrequire a more complex winding pattern.

To control the position of the windings in the outer slots, special endloops referred to herein as phase shift end loops are used. in theillustrated embodiment, each phase includes three windings that areconnected in parallel. With each winding being formed by two continuouswires that joined together at their ends to thereby form one long filarthat forms one of the parallel windings. The number of parallel windingsis one less than the number of physical slots used to form each pole.Thus, for each wrap or turn the windings make about the stator core, thethree windings can be used to fill each central slot, BB, CC and one ofthe outer slots, AA, BB as depicted in the illustrated embodiment. Byforming all three windings with a phase shift end loop at a particularspot between two poles wherein the phase shift end loops are all oneslot different than the standard pitch end loops, the wires can beshifted from the three most counterclockwise slots of each pole to thethree most clockwise slots of each pole or visa versa.

For example, in FIG. 1, at the point where wires X, Y and Z transitionfrom layer 3 to layer 4, all three end loops have a 10 pitch end loopthat function as phase shift end loops. In other words, after completingtwo wraps or turns, the wires X, Y, Z have a phase shift end loop. Thisis also seen in FIG. 4 wherein at pole 15 in layer 3, wire X is in slotAA, wire Y is in slot BB and wire Z is in slot CC as a result of the 10pitch phase shift end loops, wire X is in slot BB , wire Y is slot CCand wire Z is in slot DD at pole 16 in layer 4. In the illustratedexample, these phase shift end loops occur at the point where thewindings transition from layer 3 to layer 4. This is necessary tomaintain the pattern wherein the windings are in slot AA in layers 1, 2and 3 and are in slot DD in layers 4, 5 and 6. If an alternating patternwere employed for the two different phases in the outer slots, a largernumber of phase shift end loops would be required.

Wires A, B and C also have phase shift end loops as can be seen withreference to FIGS. 2 and 4. After completing one wrap or turn, wires A,B, C have a phase shift end loop. This can be seen in FIG. 2 where thewires A, B, C transition from layer 3 to layer 4. This is also seen inFIG. 4 wherein at pole 16 in layer 3, wire B is in slot AA, wire C is inslot BB and wire A is in slot CC as a result of the 10 pitch phase shiftend loops, wire B is in slot BB, wire C is slot CC and wire A is in slotDD at pole 1 in layer 4.

To provide an electrically balanced winding pattern, each of theparallel windings needs to be in each slot central slot, BB, CC, anequal number of times and needs to be in each outer slot, AA, DD, anequal number of times. For the illustrated embodiment, the till ratiobetween the central slots, BB, CC and the outer slots AA, DD is 2:1 and,thus, each winding needs to be disposed in the central slots twice asmany times as it is disposed in the outer slots. Position change endloops which shuffle the relative position of the windings in pole slotsare used to achieve this balance.

In the illustrated example, each set of wires A, B, C and X. Y, Z aresubject to position change end loops to alter the relative position ofthe wires at three locations for a total of six such locations. Turningfirst to FIGS. 1, 4 and 5, it can be seen that wires X, Y and Z aresubject to three position changes. At the interval between poles 8 and 9when wires X, Y and Z are in layer 1, a set of position change end loopsare used to alter the relative positions of wires X, Y and Z. At thislocation, the end loop wire X has a pitch of 11 slots while the endloops for wires Y and Z each have a pitch of 8 slots. As a result, wireX moves from slot AA at pole 8 to slot CC at pole 9, wire Y moves fromslot BB at pole 8 to slot AA at pole 9 and wire Z moves from slot CC atpole 8 to slot BB at pole 9.

Wires X, Y, Z are subject to another position change at the intervalbetween pole 8 and 9 when the wires are in layer 3. See FIGS. I and 5.This position change involves wire X having a position change end loopwith a pitch of 7 lots, wire Y having a position change end loop with apitch of 10 slots and wire Z having a position change end loop with apitch of 10 slots. As a result, in layer 3, wire X moves from slot CC atpole 8 to slot AA at pole 9, wire Y moves from slot AA at pole 8 to slotBB at pole 9 and wire Z moves from slot BB at pole 8 to slot CC at pole9.

Wires X, Y, Z are subject to a third position change at the intervalbetween poles 16 nd 1 as the wires shift from layer 4 to layer 5. SeeFIGS. 1 and 4. This position change involves wire X having a positionchange end loop with a pitch of 11 slots, wire Y having a positionchange end loop with a pitch of 8 slots and wire Z having a positionchange end loop with a pitch of 8 slots. Each of these position changeend loops also move wires X, Y, Z from layer 4 at pole 16 to layer 5 atpole 1. Thus, wire X moves from slot BB at pole 16 to slot DD at pole 1,wire Y moves from slot CC at pole 16 to slot BB at pole 1 and wire Zmoves from slot DD at pole 16 to slot CC at pole 1. To provide anelectrically balanced winding pattern, each of the parallel windingsneeds to be in each central slot BB an equal number of times, in eachcentral slot CC an equal number of times, in each outer slot AA an equalnumber of times and in each outer slot DD an equal number of times. Fora stator having more slots per pole per phase, the same pattern appliesfor the parallel wires to be electrically balanced.

Wires A, B, C are also subject to position change end loops. Morespecifically, and as can be seen in FIGS. 2 and 3, at the point wherewires A, B, C shift from layer 2 to layer 3, the end loops extendingbetween poles 15 and 16 are position change end loops. This positionchange involves wire A having a position change end loop with a pitch of11 slots, wire B having a position change end loop with a pitch of 8slots and wire C having a position change end loop with a pitch of 8slots. Each of these position change end loops also move wires A, B, Cfrom layer 2 at pole 15 to layer 3 at pole 16. Thus, wire A moves fromslot AA at pole 15 to slot CC at pole 16, wire B moves from slot BB atpole 15 to slot AA at pole 16 and wire C moves from slot CC at pole 15to slot BB at pole 16.

Wires A, B, C are subject to a second position change at the intervalbetween poles 7 and 8 in layer 4. This position change involves wire Ahaving a position change end loop with a pitch of 7 slots, wire B havinga position change end loop with a pitch of 10 slots and wire C having aposition change end loop with a pitch of 10 slots. Thus, wire A movesfrom slot DD at pole 7 to slot BB at pole 8, wire B moves from slot BBat pole 7 to slot CC at pole 8 and wire C moves from slot CC at pole 7to slot DD at pole 8.

Wires A, B, C are subject to a third position change at the intervalbetween poles 7 and 8 in layer 6. This position change involves wire Ahaving a position change end loop with a pitch of 11 slots, wire Bhaving a position change end loop with a pitch of 8 slots and wire Chaving a position change end loop with a pitch of 8 slots. Thus, wire Amoves from slot BB at pole 7 to slot DD at pole 8, wire B moves fromslot CC at pole 7 to slot BB at pole 8 and wire C moves from slot DD atpole 7 to slot CC at pole 8.

As mentioned above, the wiring diagrams in FIGS. 1 and 2 label any pitchbetween slot segments that is non-standard. The location of the numberindicating the non-standard pitch also indicates at which axial end ofthe stator the end loop forming the non-standard pitch is located. FIGS.1 and 2 also show from which axial end of the stator the beginning andend of wires A, B, C, X, Y, Z extend. As can be seen in FIG. 1, theposition change end loops for wires X, Y, Z are all at the same axialend of the stator assembly as the start and finish lead ends of wires X,Y, Z with the phase shift end loops being positioned on the oppositeaxial end of the stator assembly. Similarly, as can be seen in FIG. 2,the position change end loops for wires A, B, C are all at the sameaxial end of the stator assembly as the start and finish lead ends ofwires A, B, C with the phase shift end loops being positioned on theopposite axial end of the stator assembly. The start and finish leadends and position change end loops of wires A, B, C, Y, Z are all on thesame axial end of the stator assembly while the phase change end loopsof wires A, B, C X, Y, Z are all on the opposite side of the statorassembly.

It is additionally noted that when position change end loops are usedwith the wires, the individual wire having the largest pitch will beextended further axially than the wires with the shorter pitches andwill have an end loop that extends over the shorter pitch and axiallyshorter end loops. In other words, if three wires have position changeend loops with two wires having a pitch of 8 and one having a pitch of11, the wire having a pitch of 11 will be extended axially further fromthe stator core than the two wires with the pitch of 8 and the end loopof the wire having a pitch of 11 will extend over the other two wireshaving a pitch of 8 to thereby avoid spatial conflicts between thewires.

While the described position change end loops are used to electricallybalance the windings, it is noted that the wires A, B, C, X, Y, Z arenot individually electrically balanced but once they are seriallyconnected in pairs, the three resulting parallel windings areelectrically balanced. In other words, each winding is formed by aseries connection between two individual unbalanced wires to form abalanced winding. This is further discussed below with reference toTables 3 and 4.

The wires are connected together at their finish ends. The start end ofWire A is located in layer 1 of pole 16, from there, wire A wraps aroundthe core clockwise for 3 circumferential passes, where its finish endextends from pole 15 in layer 6. The start end of Wire Z is located inlayer 1 of pole 1, from there, wire Z wraps around the core clockwisefor 3 circumferential passes, where its finish end extends from pole 16in layer 6. The finish end of wire A is connected in series with thefinish end of wire Z by a reversing loop. The reversing loop is called areversing loop because reversing loop connects the finish end of wire Zto the finish end of wire A and if you trace the path of the resultingwinding formed by this pair of wires, the path of the winding reversesat this loop. Said another way, assume a current flows from the startend of wire Z, through the series connection and finishes at the startend of wire A. From the start end of wire Z, the current will flowclockwise around core until it reaches the reversing loop. At thereversing loop, the current will reverse direction and flowcounterclockwise around the core until it reaches start lead of wire A.

Each of the wire pairs in the exemplary embodiment are connected withsuch a reversing loop. Thus, the end of wire A extending from layer 6 atpole 15 is connected in series with the end of wire Z extending fromlayer 6 at pole 16; the end of wire B extending from layer 6 at pole 15is connected in series with the end of wire X extending from layer 6 atpole 16; and the end of wire C extending from layer 6 at pole 15 isconnected in series with the end of wire Y extending from layer 6 atpole 16. The start leads of each of the wires are connected with anexternal circuit member. For example, start leads A, B and C may all beattached to a neutral connection with start leads X, Y and Z all beingattached to a regulator, inverter or other circuit member. The startleads of the A, B and C wires all extend from layer 1 of pole 16 and areconductively coupled together, similarly, the start leads of the X, Yand Z wires all extend from layer 1 of pole 1 and are conductivelycoupled together. As a result the first winding (formed by the seriesconnected pair of wires A and Z), the second winding (formed by theseries connected pair of wires B and X), and the third winding (formedby the series connected pair of wires C and Y) are arranged in parallel.It is further noted that in the illustrated embodiment, each of theseries connections, i.e., between A and Z, between 13 and X and betweenC and Y, is also a reversing connection with one of the wires extendingin a clockwise direction about the stator from the series connection andthe other wire extending in a counterclockwise direction about thestator from the series connection.

As can be understood with reference to the tables presented below, thewinding pattern described above and shown in figures provides anelectrically balanced stator assembly.

Table 1 presented below provides a detailed summary of the windingpattern for wires A, B, C of the winding pattern for wires X, Y, Z of asingle phase of three phase electric machine 20.

TABLE 1 Winding Pattern for Wires A, B, C Slot Slot Slot Slot Slot TurnLayer Group AA BB CC DD Start 1 1 16 A B C Layer Change 1 2 1 A B C 1 22 A B C 1 2 3 A B C 1 2 4 A B C 1 2 5 A B C 1 2 6 A B C 1 2 7 A B C 1 28 A B C 1 2 9 A B C 1 2 10 A B C 1 2 11 A B C 1 2 12 A B C 1 2 13 A B C1 2 14 A B C 1 2 15 A B C Layer and Position 2 3 16 B C A Change SlotShift and 2 4 1 B C A Layer Change 2 4 2 B C A 2 4 3 B C A 2 4 4 B C A 24 5 B C A 2 4 6 B C A 2 4 7 B C A Position Change 2 4 8 A B C 2 4 9 A BC 2 4 10 A B C 2 4 11 A B C 2 4 12 A B C 2 4 13 A B C 2 4 14 A B C 2 415 A B C Layer Change 3 5 16 A B C Layer Change 3 6 1 A B C 3 6 2 A B C3 6 3 A B C 3 6 4 A B C 3 6 5 A B C 3 6 6 A B C 3 6 7 A B C PositionChange 3 6 8 B C A 3 6 9 B C A 3 6 10 B C A 3 6 11 B C A 3 6 12 B C A 36 13 B C A 3 6 14 B C A Finish 3 6 15 B C A

Table 2 presented below provides a detailed summary of the windingpattern for wires X, Y, Z of a single phase of three phase electricmachine 20.

TABLE 2 Winding Pattern for Wires X, Y, Z. Slot Slot Slot Slot Slot TurnLayer Group AA BB CC DD Start 1 1 1 X Y Z 1 1 2 X Y Z 1 1 3 X Y Z 1 1 4X Y Z 1 1 5 X Y Z 1 1 6 X Y Z 1 1 7 X Y Z 1 1 8 X Y Z Position Change 11 9 Y Z X 1 1 10 Y Z X 1 1 11 Y Z X 1 1 12 Y Z X 1 1 13 Y Z X 1 1 14 Y ZX 1 1 15 Y Z X Layer Change 1 2 16 Y Z X Layer Change 2 3 1 Y Z X 2 3 2Y Z X 2 3 3 Y Z X 2 3 4 Y Z X 2 3 5 Y Z X 2 3 6 Y Z X 2 3 7 Y Z X 2 3 8Y Z X Position Change 2 3 9 X Y Z 2 3 10 X Y Z 2 3 11 X Y Z 2 3 12 X Y Z2 3 13 X Y Z 2 3 14 X Y Z 2 3 15 X Y Z Slot Shift and 2 4 16 X Y Z LayerChange Layer Change and 3 5 1 Y Z X Position Change 3 5 2 Y Z X 3 5 3 YZ X 3 5 4 Y Z X 3 5 5 Y Z X 3 5 6 Y Z X 3 5 7 Y Z X 3 5 8 Y Z X 3 5 9 YZ X 3 5 10 Y Z X 3 5 11 Y Z X 3 5 12 Y Z X 3 5 13 Y Z X 3 5 14 Y Z X 3 515 Y Z X Layer Change and 3 6 16 Y Z X Finish

Table 3 provides a summary of the slot locations for each of wires A, B,C, X, Y, Z of a single phase of three phase electric machine 20 andillustrates how each of these individual wire are unbalanced.

TABLE 3 Slot Totals by Wire Slot AA Slot BB Slot CC Slot DD Total for A16 16 1 15 Total for B 1 31 16 0 Total for C 0 1 31 16 Total for X 15 116 16 Total for Y 16 31 1 0 Total for Z 0 16 31 1

Table 4 provides a summary of the slot locations for each of theparallel windings which are formed by a series connection between a pairof the individual wires for a single phase of three phase electricmachine 20. More specifically by joining wires A and Z into a singleelongate filar, by joining wires B and X into a single elongate filarand by joining wires C and Y into a single elongate filar. Table 4 alsodemonstrates that the three resulting windings are electricallybalanced.

TABLE 4 Slot Totals by Winding Slot AA Slot BB Slot CC Slot DD A and Z16 + 0  16 + 16  1 + 31 15 + 1 B and X 1 + 15 31 + 1  16 + 16  0 + 16 Cand Y 0 + 16  1 + 31 31 + 1  16 + 0

As can be seen from Table 4, the central to outer slot ratio for thewindings is 2:1 but, as can be understood with reference to Table 3, theratio between central slot and outer slot for the individual wires A, B,C, X, Y, Z are not 2:1. Table 4 shows how each individual unbalancedwire can be connected in series with another individual unbalanced wireto form a balanced winding.

As can also be seen in Table 4, the winding formed by the pair of wiresC and Y is arranged such that, for each pole for this winding, a firstone of the outer slots (AA or DD) is disposed on one of the clockwise orcounterclockwise sides of the central slots (BB and CC) and a second oneof the outer slots (the other one of AA or DD) is disposed on theopposite side of the central slots (BB and CC) and wherein one of thepair of continuous wires (C and Y) connected in series to form the atleast one winding has a first wire (C or Y) and a second wire (the otherone of C and Y) with the first wire being the only one of the first andsecond wires that is disposed in the first one of the outer slots andthe second wire is the only one of the first and second wires that isdisposed in the second one of the outer slots. In other words, wire C isthe only one of the pair of wires located in slot AA (which is alwayslocated on the counterclockwise side of the central slots) while wire Yis the only one of the pair of wires located in slot DD (which is alwayslocated on the clockwise side of the central slots).

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover variations, uses, or adaptations of the invention using itsgeneral principles.

What is claimed is:
 1. A multi-phase electric machine comprising: astator operably coupled with a rotor wherein the rotor is rotatablerelative to the stator; the stator including a stator core defining acentral opening and a plurality of axially extending slots whichcircumscribe the central opening; a plurality of windings mounted on thestator core wherein the plurality of windings define a plurality ofphases and wherein, for each phase, the plurality of windings include:at least two parallel windings, each winding comprising a pair ofcontinuous wires which are connected in series; wherein, for each pole,the parallel windings are disposed in one or more central slots and twoouter slots disposed on opposite sides of the central slots; eachwinding disposed in each of the central slots an equal number of timesand disposed in each of the outer slots an equal number of times andwherein each winding is disposed in each central slot twice the numberof times that the winding is disposed in each outer slot to therebydefine a slot fill ratio of 2:1 between central slots and outer slotsand wherein each wire of the wire pair forming one of the parallelwindings are disposed in the slots in a ratio that differs from the slotfill ratio.
 2. The electric machine of claim 1 wherein, for each polefor at least one winding, a first one of the outer slots is disposed onone of the clockwise or counterclockwise sides of the central slots anda second one of the outer slots is disposed on the opposite side of thecentral slots and wherein one of the pair of continuous wires connectedin series to form the at least one winding has a first wire and a secondwire with the first wire being the only one of the first and secondwires that is disposed in the first one of the outer slots.
 3. Theelectric machine of claim 2 wherein the second wire is the only one ofthe first and second wires that is disposed in the second one of theouter slots.
 4. The electric machine of claim 2 wherein each winding isdisposed in each of the slots an equal number of times.
 5. The electricmachine of claim 2 wherein the stator assembly defines a standard pitchbetween each pole of each phase, the pitch being a commoncircumferential spacing between corresponding slots of each pole; andwherein each wire includes a phase shift end loop having a pitch thatdiffers from the standard pitch by one slot, each of the parallelwindings having the phase shift end loop at the same pole locations. 6.The electric machine of claim 5 wherein the stator assembly definesfirst and second oppositely disposed axial ends, each of the windingsdefining leads connectable to an external circuit member, the leadsbeing disposed at the first axial end and the phase shift end loopsbeing disposed at the second axial end.
 7. The electric machine of claim6 wherein each wire extends for a plurality of wraps about the statorand the phase shift end loops are disposed at a location where the wiretransitions from one layer to another layer.
 8. The electric machine ofclaim 2 wherein, for each pole of each phase, a first one of the outerslots is disposed on the counterclockwise side of the central slots anda second one of the outer slots is disposed on the clockwise side of thecentral slots and wherein the wires disposed in one of the first andsecond outer slots are disposed in radially outermost layers and thewires in the other one of the first and second outer slots are disposedin radially innermost layers whereby each outer slot is filled withwires from two separate phases.
 9. The electric machine of claim 5wherein each wire includes at least one position change end loop,wherein each of the parallel windings has one of the position changeloops at the same location, wherein the position change end loops definea non-standard pitch to thereby change the relative positions of theparallel windings in the slots.
 10. The electric machine of claim 9wherein the stator assembly defines first and second oppositely disposedaxial ends, each of the windings defining leads connectable to anexternal circuit member, the leads and the position change end loopsbeing disposed at the first axial end and the phase shift end loopsbeing disposed at the second axial end.
 11. The electric machine ofclaim of claim 9 wherein each phase includes at least three windingsconnected in parallel.
 12. The electric machine of claim 11 wherein eachphase includes three parallel windings and each pole includes twocentral slots and two outer slots, each central slot being filled withsix segments of wire and each outer slot being filled with threesegments of wire.
 13. The electric machine of claim 12 wherein each wireof each winding of each phase defines one phase shift end loop and threeposition change end loops with all remaining end loops defining astandard pitch.
 14. The electric machine of claim 13 wherein the statorassembly defines first and second oppositely disposed axial ends, eachof the windings defining leads connectable to an external circuitmember, the leads and the position change end loops being disposed atthe first axial end and the phase shift end loops being disposed at thesecond axial end.
 15. The electric machine of claim 14 wherein, for eachpole of each phase, the wires disposed in one of the first and secondouter slots are disposed in radially outermost layers and the wires inthe other one of the first and second outer slots are disposed inradially innermost layers whereby each outer slot is filled with wiresfrom two separate phases.
 16. The electric machine of claim 15 whereinthe electric machine is a three phase electric machine.
 17. Amulti-phase electric machine comprising: a stator operably coupled witha rotor wherein the rotor is rotatable relative to the stator; thestator including a stator core defining a central opening and aplurality of axially extending slots which circumscribe the centralopening; a plurality of windings mounted on the stator core wherein theplurality of windings define a plurality of phases and wherein, for eachphase, the plurality of windings include: at least two parallelwindings, each winding comprising a pair of wires which are connected inseries and, wherein, for each pole, the parallel windings are disposedin one or more central slots and two outer slots disposed on oppositesides of the central slots; and wherein, for at least one winding, thepair of wires forming the winding are connected in series by a reversingloop and, for each pole for the at least one winding, a first one of theouter slots is disposed on one of the clockwise or counterclockwisesides of the central slots and a second one of the outer slots isdisposed on the opposite side of the central slots and wherein one ofthe pair of continuous wires connected by the reversing loop to form theat least one winding has a first wire and a second wire with the firstwire being the only one of the first and second wires that is disposedin the first one of the outer slots.
 18. The electric machine of claim17, wherein the second wire is the only one of the first and secondwires that is disposed in the second one of the outer slots.
 19. Theelectric machine of claim 18, wherein for at least one central slot ofone pole, the first and second wires are disposed in the same slot. 20.The electric machine of claim 19, wherein for each pole, the parallelwindings are disposed in the one or more central slots and the two outerslots disposed on opposite sides of the central slots; each windingdisposed in each of the central slots an equal number of times anddisposed in each of the outer slots an equal number of times and whereineach winding is disposed in each central slot twice the number of timesthat the winding is disposed in each outer slot to thereby define a slotfill ratio of 2:1 between central slots and outer slots and wherein eachwire of the wire pair forming one of the parallel windings are disposedin the slots in a ratio that differs from the slot fill ratio,
 21. Amulti-phase electric machine comprising: a stator operably coupled witha rotor wherein the rotor is rotatable relative to the stator; thestator including a stator core defining a central opening and aplurality of axially extending slots which circumscribe the centralopening; a plurality of windings mounted on the stator core wherein theplurality of windings define a plurality of phases and wherein, for eachphase, the plurality of windings include: at least two parallelwindings, each winding comprising a pair of wires which are connected inseries and; wherein, for each pole, the parallel windings are disposedin one or more slots; and wherein a first one of the parallel windingshas a first pair of the wires, the first pair of wires being connectedin series by a reversing loop, wherein the first one of the parallelwindings is electrically balanced and at least one wire of the firstpair of wires is electrically unbalanced.
 22. The electric machine ofclaim 21, wherein the first parallel winding is disposed in one or morecentral slots and two outer slots disposed on opposite sides of thecentral slots, and wherein, for each pole for of the first parallelwinding, a first one of the outer slots is disposed on one of theclockwise or counterclockwise sides of the central slots and a secondone of the outer slots is disposed on the opposite side of the centralslots and wherein the pair of continuous wires connected by thereversing loop to form the first parallel winding has a first wire and asecond wire with the first wire being the only one of the first andsecond wires that is disposed in the first one of the outer slots. 23.The electric machine of claim 22 wherein the second wire is the only oneof the first and second wires that is disposed in the second one of theouter slots.
 24. The electric machine of claim 21, wherein, for eachpole, the parallel windings are disposed in one or more central slotsand two outer slots disposed on opposite sides of the central slots;each winding disposed in each of the central slots an equal number oftimes and disposed in each of the outer slots an equal number of timesand wherein each winding is disposed in each central slot twice thenumber of times that the winding is disposed in each outer slot tothereby define a slot fill ratio of 2:1 between central slots and outerslots and wherein each wire of the wire pair forming one of the parallelwindings are disposed in the slots in a ratio that differs from the slotfill ratio.